Light emitting diodes (LED's) are coming into considerable use in a variety of fields and for different purposes. For example, in postage meters light emitting diodes are used as opto-isolators to convey a signal to a secured area where use of conventional wiring would be impractical. Another use is in zero crossing detector circuits wherein light emitting diodes are used to trigger a gate such as a thyristor. These are two uses that provide isolated control of a function. Another use of LED's is for the purpose of erasing residual charge on the photoconductor of a copier as is disclosed in U.S. Pat. No. 4,255,042. In none of these examples is there a need for uniformity of the intensity of the light being emitted. There are uses of LED's where the uniformity of light intensity or the amount of light incident upon a surface is a factor. As an example, where an LED array is utilized is as a printer that creates an image on a photoconductor which is to be subsequently developed, it is important that all the LED's emit light of substantially the same energy so that an essentially uniform charge is created on the photoconductor. This may be accomplished by having uniform light intensity emitted by each LED or by individually varying the time the LED's are enabled inversely to their respective light intensity.